Every stocktake comes down to the same awkward question: how much beer is actually left in that part-used keg or half-poured cask? Get it wrong and your GP is a work of fiction — you’re either writing off beer you’ve still got, or carrying stock that quietly walked out the cellar door. After fifteen years behind the pumps I’ve learned there are only two reliable ways to answer it: a dipstick or a set of scales. Here’s exactly how both work, when to use each, and how to stop guessing.
Key takeaways
- Cask ale (firkins, pins) is measured with a dipstick — a calibrated rod you dip through the shive.
- Kegs (lager, stout, keg ale) are measured by weight — weigh the keg, subtract the empty (tare) weight, convert the remainder to pints.
- A standard UK keg is 11 gallons / 50 litres; the most common cask is a 9-gallon firkin (72 pints), of which only ~66 pints are actually saleable.
- Measuring part-used containers properly is the single biggest source of GP accuracy at stocktake — and the easiest place for losses to hide.
Why measuring part-used containers matters
A full container is easy — you know what’s in it. The money is made or lost on the partials: the keg that’s two-thirds gone, the cask you tapped on Friday. If you eyeball these (“call it half”) your stock valuation drifts every single week. Across a busy cellar those guesses compound into a GP that looks fine on paper but doesn’t match the bank. Accurate partials also expose the real losses — over-pouring, line cleaning waste, ullage, and the occasional staff “freebie” — instead of burying them in a rounding error.
Running this problem at your pub?
Here's the system I use at The Teal Farm to fix it — real-time labour %, cash position, and VAT liability in one dashboard. 30-minute setup. £97 once, no monthly fees.
Get Pub Command Centre — £97 →No monthly fees. 30-day money-back guarantee. Built by a working pub landlord.
UK cask & keg sizes you’ll be measuring
| Container | Volume | Pints (gross) | Typical saleable |
|---|---|---|---|
| Pin (cask) | 4.5 gal / 20.5 L | 36 | ~33 |
| Firkin (cask) | 9 gal / 40.9 L | 72 | ~66 |
| Kilderkin (cask) | 18 gal / 81.8 L | 144 | ~134 |
| Keg | 11 gal / 50 L | 88 | ~85 |
The gap between gross and saleable matters: a 72-pint firkin only yields around 66 sellable pints once you account for sediment, finings and the bit below the tap. Build that into your expectations or every cask will look like a loss.
Method 1 — The dipstick (for cask ale)
Cask ale sits horizontally and can’t be weighed mid-service without disturbing the sediment, so the trade has used a dip rod for generations. The principle is simple: you lower a calibrated stick through the shive (the top hole) until it touches the bottom of the cask, withdraw it, and read off where the beer wetted the rod. A good dipstick is marked for standard cask sizes so it reads straight off in pints or gallons.
How to dip a cask:
- Make sure the cask has settled and is sitting level on the stillage.
- Remove the shive’s tut (or use the dip hole) and lower the rod gently and vertically until it rests on the bottom.
- Withdraw smoothly and read the wetted length against the firkin/pin scale.
- Note the figure before the liquid runs — read it quickly and consistently each week.
A purpose-made horizontal cask & keg beer dipstick takes the maths out of it — the gallon and pint graduations are printed on the rod, so you read the remaining volume directly rather than converting from a length. It’s an £8 tool that pays for itself the first time it stops you writing off beer you actually still have.
Method 2 — Weighing the keg
You can’t dip a sealed, pressurised keg, so kegs are measured by weight. The logic: beer weighs almost exactly 1 kg per litre, so if you know the full weight and the empty (tare) weight, everything in between is beer you can convert to pints.
The keg weight method:
- Find the tare (empty) weight. A standard 50 L steel keg weighs roughly 13–14 kg empty — it’s usually stamped on the keg chime. Use the real figure where you can.
- Weigh the part-used keg on a flat platform scale.
- Subtract the tare. The remainder (in kg) is roughly the litres of beer left.
- Convert to pints: litres × 1.76 = pints. So 20 kg of beer left ≈ 20 L ≈ 35 pints.
A simple keg checker / gallon measure or a flat platform scale makes this a ten-second job per keg. Once you’ve got the tare weights for your common kegs noted down, weighing partials is faster and far more accurate than any visual guess.
Method 3 — The pressure/feel shortcuts (and why they fail)
Plenty of cellars still “measure” partials by tilting the keg or judging the pour pressure. It’s better than nothing, but it’s not stocktake-grade: temperature, gas pressure and froth all throw it off. Use feel to spot a near-empty keg for changeover — use a dipstick or scales for anything you’re putting a number against.
Common mistakes that wreck your numbers
- Guessing partials. “Half a keg” is the most expensive phrase in the cellar.
- Using the wrong tare weight. Plastic and steel kegs differ by several kg — using a generic figure skews every reading.
- Forgetting ullage on cask. Always measure to saleable, not gross, volume.
- Measuring at different times. Dip and weigh at the same point each week so your figures are comparable.
Stop doing the maths by hand — let StockTap do it
The measuring is the easy part; the conversion and valuation is where time disappears and errors creep in. StockTap is the stock-take app I built for my own pub: you snap a photo or punch in the dip/weight reading and it converts to saleable pints, values the stock, and tracks your GP line by line — no spreadsheets, no mental arithmetic at 11pm. It’s a one-off £97, and it turns the awkward “how much is left?” question into a two-second entry. See how StockTap works →
Frequently asked questions
How do you measure how much beer is left in a keg?
Weigh it. Subtract the empty (tare) weight from the current weight — the difference in kilograms is roughly the litres of beer remaining. Multiply litres by 1.76 to get pints.
What is a beer dipstick and how does it work?
A dipstick is a calibrated rod you lower through the shive of a cask until it touches the bottom. The beer wets the rod, and you read the remaining volume off the printed firkin/pin scale.
How many pints are in a firkin?
A firkin holds 72 pints gross (9 imperial gallons), but only around 66 are saleable once sediment and ullage are removed.
Can you weigh a cask instead of dipping it?
You can, but it’s awkward — casks are heavy, sit horizontally, and weighing disturbs the sediment. For cask ale a dipstick is faster and more accurate; save weighing for kegs.
How accurate is weighing a keg?
Very — within a pint or two — provided you use the correct tare weight for that keg type and a level scale.
Disclosure: some links above are affiliate links to Amazon. If you buy through them I may earn a small commission at no extra cost to you. I only link to kit I’d actually use in my own cellar.
This is part of our complete guide to cask ale wastage and loss control — where cask money disappears and how to protect your GP.
See also our UK keg guide — the top draught beers, pints per keg, and how to work out the GP on every line.
Running your pub on gut feel?
The Pub Command Centre gives you wet GP%, cellar checks, staff cost and weekly P&L — from your phone, every shift. £97 once. No subscription.
See the Pub Command Centre →